1. Field of Invention
The present invention relates to a control method of a fan rotation speed and in particular to a control method of the fan rotation speed of a serial-connected fan set.
2. Related Art
Recently, the data process amount and speed in the electronic device are dramatically increased. Besides, the electronic device may contain more and more components due to the development of the integrated processes. Thus, the heat dissipation of the electronic device becomes more and more important. The main solution for heat dissipation is to configure a fan for increasing the air convection so as to prevent the heat accumulation in the electronic device.
The conventional fan control method is to limit the rotation speed of the fan, so that the fan can be operated under the constant voltage or wide voltage and have improved properties, thereby protecting the control circuit. When the fans are connected in series, the rotation speed of the downstream fan, which is closer to the outlet, may increase due to the effect of the upstream fan. However, the conventional fan control method of limiting the rotation speed of the fan may limit the rotation speed of the downstream fan, so that the entire properties of the serial-connected fans are impacted. Thus, the heat dissipation ability based on the conventional fan control method is decreased. Although some commercial serial-connected fans can remove the upper limitation for the rotation speed of the downstream fan, the component preparing and manufacturing become more complex and difficult. In addition, when the install direction of the serial-connected fan is reversed, the desired effect fails.
Therefore, it is one of important subjects of the present invention to provide a control method of the fan rotation speed that can control the fans in multiple modes, so that the fans can be controlled in different modes during different operation sections or environments. Thus, the serial-connected fan set can provide the maximum performance, and the control circuit can be protected from being burned out due to the excess power.